Rotary disc filters are used to remove suspended solids from water. Influent water flows into a drum and from the drum into a series of disc-shaped filter members secured around the drum. From the disc-shaped filter members, the water flows outwardly through filter media disposed on opposite sides of the disc-shaped filter members. Suspended solids in the water are captured on the interior surfaces of the filter media. From time-to-time, the suspended solids are removed from the interior surfaces of the filter media. This is achieved by rotating the filter media to an upper cleaning position and backwashing the filter media. A pressurized backwash is sprayed onto the exterior surfaces of the filter media, discharging the suspended solids into a trough disposed in the drum. The suspended solids are then discharged from the trough and the disc filter.
To control head pressure in the disc filter, some of the influent water may be diverted from the drum and the disc-shaped filter members. This diverted water is referred to as bypass water. Frame-type disc filters are typically supported on a concrete structure that includes a built-in basin for receiving filtered water. In some cases, the bypass water overflows the inlet to the disc filter into the basin. This presents a backwash problem. Filtered water collected in the basin of the underlying support structure is typically used for the backwash. It is appreciated that the bypass water is unfiltered and hence includes suspended solids. Therefore, when the bypass water is mixed with the filtered water and this mixture is used to backwash the filter media, it is appreciated that the suspended solids in the backwash tends to clog upstream strainers that are employed to protect the backwash nozzles. In other cases, the backwash water is directly discharged from the disc filter. That is, the bypass water is separately discharged from the disc filter without combining the bypass water with the filtrate in the basin of the support structure. This is often an expensive solution that is disfavored by end users. In order to implement this solution, one must provide a separate pipe or another concrete channel in order to channel the bypass water downstream of the disc filter where the bypass water can be mixed with the disc filter effluent or filtered water.
Therefore, there has been and continues to be a need for a practical and cost effective way of handling bypass water in frame-type disc filters.